The present invention relates to exterior insulation and finish systems and building walls including an enhanced thickness fabric that is useful in reinforcing a matrix of exterior finishing materials, and especially, to a corrosion resistant lath for supporting exterior finishing materials, such as stucco.
Hard coat stucco has been in use since ancient time, while synthetic stuccos and exterior insulation and finishing systems (“EIFS”) have been used on construction in North America and Europe since World War II. The most common EIFS is formed around a polystyrene board which is adhered or fastened to a substrate, such as oriented strand board (“OSB”) gypsum or plywood sheathing. The polystyrene board is then coated with a “base coat” layer of at least 1/16 inch in thickness which contains cement mixed with an acrylic polymer. The base coat is generally layered with an embedded glass fiber reinforced mesh which helps to reinforce it against cracking. A “finish coat”, typically at least 1/16 inch or more in thickness, is either sprayed, troweled, or rolled onto the base coat. The finish coat typically provides the color and texture for the structure.
For stucco applications, the lath or wire mesh is typically applied to the surface of the polystyrene board, or any other surface that would otherwise not provide adequate mechanical keying for the stucco. Metal-lath reinforcement is often used whenever stucco is applied over open frame construction, sheathed frame construction, or a solid base having a surface that provides an unsatisfactory bond. When applied over frame construction, the two base coats of plaster should have a total thickness of approximately ⅜ to approximately ¾ inches (19 mm) to produce a solid base for the decorative finish coat.
Metal lath reinforcement is also recommended for the application of stucco and plaster to old concrete or masonry walls, especially if the surface has been contaminated, or is lacking in compatibility with the base layer. There are also plastic laths available for the same purpose.
According to the International Conference of Building Officials Acceptance Criteria for Cementitious Exterior Wall Coatings, AC 11, effective Oct. 1, 2002, and evaluation report NER-676, issued Jul. 1, 2003, wire fabric lath should be a minimum of No. 20 gauge, 1 inch (25.4 mm) (spacing) galvanized steel woven-wire fabric. The lath must be self-furred, or furred when applied over all substrates except unbacked polystyrene board. Self-furring lath for coatings must comply with the following requirements: (1) the maximum total coating thickness of ½ inch (25.4-50.8 mm); (2) furring crimps must be provided at maximum 6 inch intervals each way; and (3) the crimps must fur the body of the lath a minimum of ⅛ inch (3.18 mm) from the substrate after installation. In addition to the NER-676 code, lath for stucco systems typically must be at least 0.125 inches thick in order to meet the building codes for metal lath (ASTM C847-95), for welded wire lath (ASTM C933-96A), and for woven wire plaster base (ASTM C1032-96).
While galvanized metal lath can substantially prevent stucco from sloughing or sagging until it has set, it contains steel which can eventually rust and cause discoloration in the finish coat. In fact, one drawback of metal lath for use in stucco in shore communities is that salt water and driving rain accelerate the corrosion of steel components. Another drawback to wire lath is that cutting and furring often exposes sharp metal wire which can penetrate the skin or a glove of a construction worker.
Accordingly, there remains a need for an improved lath for stucco systems which is corrosion resistant and easier to install with a minimal risk of injury.